The present invention relates to a steering gear for pivotal wheels on a vehicle or carriage, wherein the steering gear is adapted to steer the pivotal wheels so that the centre lines in the rotational axes for the pivotal and possible non-pivotal wheels meet in a common point which is the pivot point of the carriage, and wherein the vertical pivot axle of each of the pivotal wheels is provided with at least one chain wheel or belt pulley, each of said chain wheels/belt pulleys being connected with a chain wheel/belt pulley assigned to the pivot axle of another laterally positioned pivotal wheel by means of a chain or a belt, so that the pivot angle swing is transferred between the pivotal wheels.
The vehicle or the carriage, respectively, comprises in each single case a set of travelling wheels including at least two, preferably four or more, pivotal, steerable travelling wheels.
The steering gear is intended used on a vehicle/carriage having a plurality of steerable wheels, for the conveyance of long, heavy objects, such as loaded 40 feet containers. When driving on small quay and dock plants as well as within buildings, it is necessary that the carriage has several steerable wheels with a minimum pivot radius (90xc2x0 to either side).
In a set of travelling wheels of a vehicle/carriage comprising in all six travelling wheels: two steerable front wheels, two steerable intermediate wheels and two non-steerable rear wheels, the mutually differing angular deflections of the individual travelling wheels upon turning of the vehicle may be illustrated as follows: The fixed rotational axis of the rear wheels is extended imaginarily, and an imaginary line is drawn from the rotational axis of one of the steerable wheels (e.g. the right hand front wheel) until it crosses the rotational axis extension of the rear wheels. Thus, a crossing point is created, the location thereof on said rotational axis extension is dependent on the radius of the turn; the more sudden turn, the closer to the rear wheels is the crossing point situated. This crossing point constitutes the turning centre of all pivotable, steerable wheels, and this pre-supposes, of course, that all four steerable travelling wheels in the present exemplary embodiment each exhibits an angular deflection differing from the angular deflection of each of the remaining three travelling wheels.
The angle between an imaginary line parallel to the rotational axis of the rear wheels and the rotational axis of the various steerable wheels will differ from wheel to wheel in any turning position of the vehicle/carriage. (In one case, said angles were: right hand front wheel: xcex1126 75xc2x0; left hand front wheel: xcex12≈67xc2x0; right hand intermediate wheel: xcex13≈60xc2x0; left hand intermediate wheel: xcex14≈53xc2x0)
When following the road ahead, all angles xcex11-xcex14 are each equal to 90xc2x0 (the wheels are parallel).
The above-mentioned case where the turning radius through the mid point of respective wheels of all pivotable, steerable travelling wheels passes through a common point, represents the ideal case.
In order to secure correct angular deflection at each single pivotable, steerable wheel upon turning of the vehicle/carriage, the steering angles (xcex1) are synchronised by means of a steering gear always securing correct angle of the wheel axes in relation to the rolling direction of the wheels.
Correct angular deflection/steering angle for all pivotable, steerable travelling wheels is characterized in that all centre lines for the wheel rotation have said common crossing point or are parallel (upon driving ahead/reversing).
Today, on loading and passenger vehicles, a synchronising mechanism comprising steering-gear levers and lateral struts is used for synchronising the turning movements of the steerable travelling wheels. A disadvantage of this prior art synchronising mechanism is that the inaccuracy adjacent maximum angular deflections is all too large.
Moreover, it does not allow full swing-out of the steering wheels. Thus, said swing-out will never approach 90xc2x0 to either side. For vehicles and carriages having a need for approximately 90xc2x0 turning possibility to either side, e.g. the above-mentioned construction where the set of travelling wheels comprises two steerable front wheels, two or more steerable intermediate wheels, as well as two rear wheels having a fixed rotational axis, this known synchronising mechanism is less fit.
In a vehicle having a 90xc2x0 turning possibility to either side, the pivotable, steerable wheels must be driven; preferably hydraulic or electric operation. This has become more and more usual, e.g. in special vehicles within agriculture and industry.
Moreover, prior art comprises in the field concerned, e.g. those mechanisms disclosed in Swedish Laying-Out publication No. 343,254, British patent specification No. 1,155,469 as well as British patent applications Nos. 2,116,131 and 2,155,870.
The Swedish Laying-out publication No. 343,254 deals with a steering gear which is intended to be used on steerable portal cranes. Here, the steering movement is transferred to the wheels from a rack through a toothed segment. The racks are displaced by means of cam grooves (called slideways). The shape of the cam grooves (the slideways) is configurated such that the racks, through the toothed segments, allot to the guide wheels differing steering angles in relation to the driving direction of the vehicle. The critical point of this known steering gear is the shape of the two cam grooves (the slideways). The shape of cam grooves cannot be calculated mathematically, and must be adapted by tests. This known steering gear is likely to be too inaccurate, especially in connection with large turning angles, e.g. up to 90xc2x0 deflection to either side. The steering mechanism has many mechanical parts which will probably be difficult and expensive to produce.
Moreover, the mechanism would not be usable in connection with two or more steerable intermediate wheels.
British patent specification No. 1,155,469 deals with a camera carriage which, in one embodiment, has four pair of wheels each allotted a vertical shaft for turning around the axis thereof in the horizontal plane. On each of the various vertical shafts, a chain wheel is mounted, two chain wheels being interconnected with an outer, driven chain wheel through a first chain, while the two chain wheels are interconnected with another chain which, through guides, likewise engages said outer, driven chain wheel.
In this known transmission mechanism, each chain wheel is circular, and it is, therefore, unfit for use in a set of wheels wherein the steerable wheels have to be allotted mutually differing angular deflections upon turning of the vehicle/carriage. With the known transmission mechanism, each wheel""s angular deflection would be equal to the remaining deflections. Therefore, upon turning it will arise lateral sliding between the wheels.
British patent application No. 2,116,131 deals with a steerable platform for a lawn mower. In this known device, the vertical shaft of each wheel is provided with pulley. The pulleys are motion-transmittingly interconnected by means of a belt driven by means of an outer, driven pulley. The pulleys have the same size and will, thus, not be usable for a is set of wheels comprising two steerable front wheels and at least one steerable intermediate wheel, spaced from the front wheels in the longitudinal direction of the vehicle and, possibly, a pair of rear wheels without turnability.
British patent application No. 2,155,870 which is intended to be used for fork truck or harvesting vehicle for agricultural purposes, deals with two different mechanisms for the provision of differing rotational movement for two wheels of a pair, each wheel""s vertical shaft being provided with a noncircular, rounded body which is comma-shaped or consists of two rounded bodies consisting of upright cones, the one with the smallest base lowermost, and the other in an opposite position. Both the comma mechanism and the cone mechanism are motion transmittingly connected by means of an endless, flexible rope. When a first wheel""s vertical shaft is rotated for turning the vehicle, the flexible rope attends to rotate the other wheel""s vertical shaft, the rotational angle of the latter shaft and, thus, of the wheel belonging thereto will differ from the rotational angle (angular deflection) of the first wheel.
On each of the comma-sign-shaped xe2x80x9crope sheavesxe2x80x9d, the ends must be bent up or down in order to prevent that these ends in an outer position touch the transfer belts. On the cone-shaped casters, helical grooves (coarse threads) have been made, said grooves upon turning (rotation) guide the transfer belts up or down along the cones and, thus, changes the diameter of the grooves.
Thus, British patent application GB No. 2,155,870 discloses two embodiments which theoretically will give two interconnected guide wheels a non-uniform guide angle when the carriage turns. It is less likely that practically usable calculation formulae can be developed, capable of defining dimensional criterions for the shape of the comma as well as the upward and downward bending of the ends of the comma. (Calculation formulae based on wheel spacings, wheel angles and distance to common turning point for all wheels on the carriage).
Calculation formulae for the shape of the cone as well as the thread pitch of the helically shaped grooves, should probably be easier to develop than for the shape of the comma, but the large building height of the cones is limiting for the practical use.
Comma-shaped or cone-shaped transfer means would hardly (due to inaccuracy and space considerations) be usable on a long vehicle for heavy transport, for steering a number (two rows) of steerable intermediate wheels, as the task is for the present invention.
Thus, the invention is occupied with a steering gear for steering angular deflections of the pivotable, steerable travelling wheels of a vehicle/carriage upon turning so that correct mutually differing deflections are secured on the individual steerable wheels, wherein the vehicle/carriage comprises a set of travelling wheels including at least two, preferably four or more pivotable, steerable travelling wheels, inclusive of a pair of front wheels, and wherein each of the vertical shafts assigned to the front wheels carries at least one non-circular, rounded means, said means which are identical, are motion transmittingly interconnected by means of a movable endless means passed around the non-circular means which, upon turning, allot the two front wheels different angular deflections. Upon turning, one wheel""s vertical shaft is influenced by turning, or the influence may take place by attacking on the endless transmission means.
According to the invention, a steering gear of the kind as defined in the last section is characterized in that interconnected chain wheels/belt pulleys which in general is to be given different angular deflections upon turning, are shaped as ellipses, the major axes thereof being disposed in a certain mutual angle when the wheel axes are parallel, i.e. that the vehicle/carriage is driven straight ahead or backwards. To the same vertical steering shafts, a non-circular means has been mounted, said means, at either side of the carriage, each is assigned an identical non-circular means on the vertical turning shafts for the steerable intermediate wheels.
The non-circular means of said intermediate wheels is by means of a second or a second and a third, respectively, endless chain/(toothed) belt, motion transferringly interconnected with identical non-circular means of steering wheels (front wheels/intermediate wheels) situated in front thereof (elliptical chain wheels or belt pulleys, preferably toothed belt pulleys, respectively, of front wheels or intermediate wheels situated in front thereof, respectively).
Such a steering gear comprising transmission devices where elliptical chain wheels/toothed belt pulleys are disposed on the vertical shafts assigned to the respective pivotable, steerable travelling wheels, enables the turning of each wheel about an individual vertical rotational axis, said pivotable, steerable wheels being interconnected in pairs by means of endless chain/toothed belt (the two front wheels being interconnected as known per se; one of the front wheels and one or more intermediate wheels being interconnected at the same side of the vehicle/carriage, each front wheel and an intermediate wheel or more on the opposite side of the side where the associated front wheel is placed, respectively).
Typically, the set of travelling wheels comprises in all six wheels, a pair of pivotable, steerable front wheels, a pair of pivotable, steerable intermediate wheels and a pair of rear wheels having a fixed rotational axis. Each of the two front wheels is assigned a vertical shaft to which is mounted elliptical chain wheels/(toothed) belt pulleys. First non-circular transmission means belonging to the front wheels and positioned at the same level, are interconnected by means of a first endless chain/(toothed) belt. Moreover, left hand front wheel""s second elliptical chain wheel/(toothed) belt pulley, at another level, is connected to left hand intermediate wheel""s elliptical chain wheel/(toothed) belt pulley by means of a second endless chain/(toothed) belt. Right hand front wheel""s second elliptical chain wheel/(toothed) belt pulley is connected with right hand intermediate wheel""s elliptical chain wheel/(toothed) belt pulley, both of which are situated at the same level as the elliptical chain wheels/belt pulleys of left hand front wheel and left hand intermediate wheel.
A steering gear which, according to the invention, comprises transmission devices based on elliptical chain wheels/(toothed) belt pulleys assigned to a plurality of pivotable, steerable wheels at either side of the carriage (having one or more elliptical chain wheels/(toothed) belt pulleys mounted on the respective vertical rotational shafts, connected in pairs by means of endless chains/(toothed) belts), has be found to give more accurate angular deflections for the pivotable wheels than achievable by means of prior art technique, especially upon sudden turns (45-90xc2x0) where steering gears shaped and designed in accordance with prior art would be quite inadequate.
Therefore, it has been a specific object of the present invention to provide a precision steering gear for vehicles/carriages constructed with a view to make 90xc2x0 turns. Upon such a sudden turn, the common intersection point of the turning radii of the steerable wheels on a fixed rear wheel axis (extension) will, with a set of travelling wheels comprising e.g. six wheels, be positioned on that rear wheel""s central point in vertical projection situated at that side towards which one is turning. Thus, if one turns 90xc2x0 to the right, said intersection point will be positioned on the vertical central line of right hand rear wheel, and right hand front wheel""s central vertical plane will form 90xc2x0 with a vertical plane through the vertical central lines of right hand rear wheel and right hand front wheel. Right hand intermediate wheel""s vertical central plane takes the same orientation as right hand front wheel, while the central vertical planes of left hand front wheel and left hand intermediate wheel form angles with the vertical plane through the vertical central line of right hand front wheel and rear wheel differing from 90xc2x0; and from each other (because their turning radii form an acute angle with each other, corresponding to general symmetry requirements in order to enable a 90xc2x0 turn to both sides).
Also, the invention would be usable on vehicles having steerable front wheels and rear wheels guided simultaneously, as well as on vehicles having four or more steerable intermediate wheels. Then, the line for a common point of intersection for the turning centres of all wheels is an imaginary line through the central point of the carriage. (This line may also be centre line for fixed, non-steerable wheels in the middle of the carriage).
Thus, a steering gear according to the invention represents a technical progress within the field concerned, especially in vehicles/carriages the set of wheels thereof allowing 90xc2x0 turns to both sides.
If the distance between the rotational axes of the front wheels and the rear wheels, upon driving straight ahead or rearwardly, respectively, is denoted C, and the corresponding distance between front wheels and intermediate wheels is denoted B, the proportion C/B willxe2x80x94in order to secure correct angular deflections for the individual guiding wheelsxe2x80x94require elliptical chain wheels/toothed belt pulleys wherein the ellipsis has a certain eccentricity or proportion (Dm/dm), respectively, between the major axis (Dm) and the small axis (dm) for the respective ellipsis. It is quite simple to construct chain wheels/toothed belt pulleys each having an elliptic efficient circumference and varying ellipsis eccentricity respectively varying the proportion Dm/dm for adoption to various proportions of C/B.